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Lower rates of embryo implantation may be due to female obesity

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 Lower rates of embryo implantation may be due to female obesity

A recent analysis conducted by researchers at the European Society of Human Reproduction and Embryology suggests that obesity in women can compromise the success of IVF treatment. The study results, presented at the annual meeting of ESHRE by the Spanish gynecologist Dr Jose Bellver, show that excessive weight impairs human reproductivity and that one of the mechanisms involved is reduced uterine receptivity. One important conclusion of the study is that women who want to undergo in vitro fertilization treatment should first lose weight.

The negative effects of overweight on assisted reproduction have been highlighted in several studies so far. The reasons given were that overweight affects menstrual regularity and ovulation. An example is polycystic ovary syndrome, the most common cause of anovulation, in which the body weight plays an essential role. The researchers came to the conclusion that obesity influence in a negative way IVF after analyzing almost 10 000 egg donation treatments conducted at three clinics in Spain between 2000 and 2011. All egg donors had normal weight but egg recipients had different body weights. The latter were divided into four groups: lean ( 1458 patients, 15.2%), normal (5706 patients, 59.5%), overweight (1770 patients, 18.5%), and obese (653 patients, 6.8%). Division into four categories was made according to BMI. Results showed that not only rates of embryo implantation but also pregnancy, twin pregnancy and live birth were  reduced as BMI increased.

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Dr Bellver said the results show that the chances of having children by egg donation are reduced by about a third for obese women. These women who received eggs from women (with normal weight) had 23% lower implantation rates than normal weight women. Dr Bellver explained that obesity is a systemic disease (ie affecting the whole body) that affects the reproductive system. Two of the mechanisms that explain the link between obesity and reproductive system are hyperandrogenism and insulin resistance, which are part of the polycystic ovarian syndrome.

Polycystic ovary syndrome is an endocrine dysfunction with an unknown cause characterized by chronic anovulation, hyperandrogenism and metabolic disorders (insulin resistance). Hyperandrogenism, ie high levels of androgens in the blood, cause acne, hirsutism, alopecia etc.. Dr Bellver explained that even in ovulatory obese women conception rates are reduced and that ovulation is not the only mechanism that justify this poor outcome. Oocyte and embryo quality seem to be affected also, but it is not yet clearly known by what mechanism. “The clinical evidence is now strong enough for implementing preconceptional health policies for obese patients considering assisted reproduction,” Dr Bellver concluded.